JP2011028947A - Separator for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery, capable of improving shutdown characteristics, heat resistance, flame retardance, and also cycle characteristics of a battery. <P>SOLUTION: The separator for the nonaqueous secondary battery includes a porus base material formed by containing thermoplastic resin, and a heat-resistant porus layer formed by containing heat-resistant resin and laminated on one surface or both surfaces of the base material. The heat-resistant porus layer includes inorganic filler which generates endoergic reaction at 200-400°C. The inorganic filler contains water-soluble sodium in an amount of 1-300 ppm in terms of a weight of Na<SB>2</SB>O. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery, and more particularly to a technique for improving the safety and battery characteristics of the non-aqueous secondary battery.

  Non-aqueous secondary batteries represented by lithium ion secondary batteries have high energy density and are widely used as main power sources for portable electronic devices such as mobile phones and notebook computers. The lithium ion secondary battery is required to have a higher energy density, but ensuring safety is a technical issue.

  The role of the separator is important in ensuring the safety of the lithium ion secondary battery, and at present, a polyethylene microporous membrane is used from the viewpoint of high strength and a shutdown function. Here, the shutdown function refers to a function of blocking the current by closing the pores of the microporous membrane when the temperature of the battery rises. This function suppresses heat generation of the battery and prevents thermal runaway of the battery.

  However, even if the pores of the microporous membrane are blocked due to the temperature rise and the current is interrupted once, if the battery temperature exceeds the melting point of polyethylene constituting the microporous membrane and exceeds the heat resistance limit of polyethylene, the microporous membrane The film itself melts and deforms and the shutdown function is lost. As a result, thermal runaway of the battery occurs, and there is a risk that the apparatus incorporating the lithium ion secondary battery may be destroyed or an accident may occur due to ignition. For this reason, in order to ensure further safety, the separator is required to have heat resistance in addition to the shutdown function.

  Thus, conventionally, a separator for a non-aqueous secondary battery in which the surface of a polyethylene microporous film is coated with a heat-resistant porous layer made of a heat-resistant polymer such as wholly aromatic polyamide has been proposed (for example, Patent Documents 1 and 2). reference). Patent Document 1 discloses a configuration in which inorganic fine particles such as alumina are included in a heat-resistant porous layer to improve heat resistance in addition to a shutdown function. Patent Document 2 discloses a configuration in which metal hydroxide particles such as aluminum hydroxide are included in the heat-resistant porous layer to improve the flame retardancy in addition to the shutdown function and heat resistance. . Any of these configurations can be expected to have an excellent effect in terms of battery safety in terms of both a shutdown function and heat resistance.

  By the way, in order to ensure the safety of the non-aqueous secondary battery, the shutdown function and heat resistance of the separator are important aspects, but flame retardancy is also important separately from the viewpoint of ignition. Current separators for non-aqueous secondary batteries often use a polyethylene microporous membrane in consideration of shutdown characteristics as described above, but polyethylene is a polymer that is easily combusted, so in the battery configuration using it. Requires special consideration for heat resistance and flame retardancy.

  However, the configuration using a metal oxide such as alumina for the heat-resistant porous layer as in Patent Document 1 is not effective in terms of flame retardancy. In that respect, if it is the structure using metal hydroxides, such as aluminum hydroxide like patent document 2, since the dehydration reaction accompanied by endothermic reaction will arise by exposing to high temperature, the improvement effect of a flame retardance will occur. I can expect.

  However, since inorganic fillers such as aluminum hydroxide generally contain water-soluble sodium derived from the production method, such water-soluble sodium may adversely affect the cycle characteristics of the non-aqueous secondary battery. There is.

International Publication No. 2008/062727 Pamphlet International Publication No. 2008/156033 Pamphlet

  Accordingly, an object of the present invention is to provide a separator for a non-aqueous secondary battery that can further improve the cycle characteristics of the battery in addition to the shutdown characteristics, heat resistance, and flame retardancy.

  As a result of intensive studies in order to solve the above problems, the present inventor has found that the above problems can be solved when the amount of water-soluble sodium contained in the flame-retardant inorganic filler is within a predetermined range. That is, the present invention adopts the following configuration.

1. A non-aqueous secondary battery comprising a porous substrate formed containing a thermoplastic resin and a heat-resistant porous layer formed containing a heat-resistant resin and laminated on one or both sides of the substrate The heat-resistant porous layer contains an inorganic filler that generates an endothermic reaction at 200 to 400 ° C., and the inorganic filler contains 1 to 300 ppm of water in terms of Na ₂ O weight. A non-aqueous secondary battery separator characterized by comprising sodium hydroxide.
2. 2. The separator for a non-aqueous secondary battery according to 1 above, wherein the inorganic filler is made of a metal hydroxide.
3. 3. The separator for a non-aqueous secondary battery according to 1 or 2 above, wherein the metal hydroxide is aluminum hydroxide or magnesium hydroxide.
4). Content of the said inorganic filler in the said heat resistant porous layer is 50 to 95 weight%, The separator for non-aqueous secondary batteries in any one of said 1-3 characterized by the above-mentioned.
5. Any one of the above 1 to 4, wherein the heat resistant resin is at least one resin selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. A separator for a non-aqueous secondary battery according to 1.
6). The separator for a non-aqueous secondary battery according to any one of the above 1 to 5, wherein the thermoplastic resin is a polyolefin.
7). A non-aqueous secondary battery for obtaining an electromotive force by doping or dedoping of lithium, wherein the non-aqueous secondary battery separator according to any one of the above 1 to 6 is used. .

  The present invention can provide a separator for a non-aqueous secondary battery that can further improve the cycle characteristics of the battery in addition to the shutdown characteristics, heat resistance, and flame retardancy. According to such a separator of the present invention, the safety and battery characteristics of a non-aqueous secondary battery can be improved.

[Separator for non-aqueous secondary battery]
The separator for a non-aqueous secondary battery of the present invention includes a porous base material formed by including a thermoplastic resin, and a heat-resistant porous material formed by including a heat-resistant resin and laminated on one or both surfaces of the base material. A separator for a non-aqueous secondary battery comprising a porous layer, wherein the heat-resistant porous layer contains an inorganic filler that generates an endothermic reaction at 200 to 400 ° C., and the inorganic filler includes: It contains 1 to 300 ppm of water-soluble sodium in terms of Na ₂ O weight.

According to such a separator for a non-aqueous secondary battery of the present invention, a shutdown function can be obtained by the base material, and a heat resistant porous layer can obtain heat resistance that does not melt even at a temperature higher than the shutdown temperature. it can. In addition, since the heat-resistant porous layer contains an inorganic filler that generates an endothermic reaction at 200 to 400 ° C., the endothermic reaction occurs when the battery is exposed to a high temperature of 200 to 400 ° C. Can be demonstrated. Then, in the separator of the present invention, since the water-soluble sodium 1~300ppm in the inorganic filler (Na 2 _O weight Conversion) is included, it is possible to improve the cycle characteristics of the nonaqueous secondary battery. Therefore, according to the separator of the present invention, a nonaqueous secondary battery excellent in safety and battery characteristics can be obtained.

Here, in the present invention, as described above, it is important that the inorganic filler contains 1 to 300 ppm (in terms of Na ₂ O weight) of water-soluble sodium. Furthermore, the content of water-soluble sodium in the inorganic filler is preferably 1 to 100 ppm, and particularly preferably 1 to 49 ppm, in terms of Na ₂ O weight. When the content of water-soluble sodium is less than 1 ppm, the effect of renewing and removing the SEI (Solid Electrolyte Interface) film formed on the negative electrode surface with water-soluble sodium cannot be obtained, and the battery has good cycle characteristics. Can't get. Moreover, when there is more content of water-soluble sodium than 300 ppm, since the ionic conduction of electrolyte solution will be inhibited and the cycling characteristics of a battery may fall remarkably, it is unpreferable.

  In this regard, Japanese Patent Application Laid-Open No. 2009-32667 describes that if the amount of Na contained in the separator is 1000 ppm or less, the cycle characteristics are not adversely affected. Thus, it can be predicted to some extent from technical common sense that the smaller the content of Na, which is an impurity, the smaller the adverse effect on the cycle characteristics. However, in the present invention, when the water-soluble sodium as an impurity is almost zero, the effect of renewing and removing the SEI film on the negative electrode interface due to the water-soluble sodium cannot be obtained, and the cycle characteristics of the battery Has been found to decrease significantly. Therefore, the present patent document does not disclose the knowledge that the state of the SEI film at the negative electrode interface is improved due to the presence of a trace amount of Na, or the technically meaningful lower limit of the Na content. Is very different. In addition, in the said literature, although the example using boehmite as an inorganic filler is shown, boehmite does not produce an endothermic reaction in 200-400 degreeC, and the flame-retardant effect like this invention is not acquired.

In the present invention, the content of water-soluble sodium in the inorganic filler is measured by measuring the concentration of Na ₂ O (sodium oxide) dissolved in water by immersing the inorganic filler in pure water at 80 ° C. for 2 hours, It can be determined from the weight ratio of the inorganic filler. In addition, the water-soluble sodium contained in the inorganic filler is not particularly limited as long as it is soluble in water as sodium ions. For example, Na ₂ O, NaOH, Na ₂ CO ₃ , NaHCO ₃ , NaCl etc. are mentioned. In addition, adjustment of the content of water-soluble sodium is not particularly required if the content is within the range of the present invention in the raw material state, but the inorganic filler contains more than 300 ppm of water-soluble sodium in the raw material state. For example, the inorganic filler can be adjusted by washing in pure water and drying after filtration.

  The inorganic filler in the present invention is not particularly limited as long as it causes an endothermic reaction at 200 to 400 ° C., but is, for example, an inorganic filler made of a metal hydroxide, a boron salt compound, a clay mineral, or the like, Those that cause an endothermic reaction at 400 ° C. are exemplified. Specific examples include aluminum hydroxide, magnesium hydroxide, calcium aluminate, dosonite, zinc borate and the like, and these can be used alone or in combination of two or more. In addition, these flame retardant inorganic fillers are appropriately mixed with other inorganic fillers such as metal oxides such as alumina, zirconia, silica, magnesia, and titania, metal nitrides, metal carbides, and metal carbonates. You can also.

  Here, in the non-aqueous secondary battery, heat generation accompanying the decomposition of the positive electrode is considered to be the most dangerous, and this decomposition occurs in the vicinity of 300 ° C. For this reason, if the generation | occurrence | production temperature of endothermic reaction is the range of 200 to 400 degreeC, it is effective in preventing the heat_generation | fever of a non-aqueous secondary battery. It should be noted that at 200 ° C. or higher, since the negative electrode almost loses its activity, it does not react with water generated from the metal hydroxide to cause heat generation and is safe. Moreover, when the endothermic reaction temperature of an inorganic filler exceeds 400 degreeC, since there exists a possibility that the heat_generation | fever of a non-aqueous secondary battery cannot be prevented suitably, it is unpreferable. For example, aluminum hydroxide, dawsonite, and calcium aluminate undergo a dehydration reaction in the range of 200 to 300 ° C, and magnesium hydroxide and zinc borate undergo a dehydration reaction in the range of 300 to 400 ° C. It is preferable to use at least one of them.

  In particular, in the present invention, the inorganic filler is preferably made of a metal hydroxide. Since the metal hydroxide undergoes a dehydration reaction accompanied by a large endotherm by heating, an effect of improving flame retardancy due to both the release of water and endotherm can be obtained. The release of water is effective in diluting the flammable electrolyte and making the battery itself incombustible. In addition, since metal hydroxide is a softer material than metal oxides such as alumina, the parts used in each process at the time of manufacturing are worn by the inorganic filler contained in the separator. There is no problem. In addition, when a metal hydroxide such as aluminum hydroxide or magnesium hydroxide is added to the heat-resistant porous layer, the charged charge decays quickly, so that the charge can be kept at a low level and handling properties are improved. Is improved. Furthermore, aluminum hydroxide and magnesium hydroxide have the function of adsorbing and co-precipitating hydrofluoric acid, so it is possible to maintain the hydrofluoric acid concentration in the electrolyte at a low level, and the durability of non-aqueous secondary batteries Can be improved. Therefore, the inorganic filler is preferably a metal hydroxide, and particularly preferably aluminum hydroxide or magnesium hydroxide. In general, the metal hydroxide contains a large amount of water-soluble sodium derived from the production method.

  In the present invention, the average particle size of the inorganic filler is preferably in the range of 0.1 to 2 μm. When the average particle diameter of the inorganic filler exceeds 2 μm, the short circuit resistance at high temperature of the heat resistant porous layer is lowered, which is not preferable. Further, there is a problem that it hinders the formation of the heat-resistant porous layer with an appropriate thickness. Further, when the average particle size of the inorganic filler is smaller than 0.1 μm, not only the coating strength is reduced and the problem of powder falling occurs, but it is substantially difficult to use such a small one from the viewpoint of cost. It is.

  In this invention, it is preferable that content of the inorganic filler in a heat resistant porous layer is 50 to 95 weight%. If the content of the inorganic filler is less than 50% by weight, the effect of improving heat resistance by the inorganic filler may not be sufficiently obtained, which is not preferable. On the other hand, if the content of the inorganic filler exceeds 95% by weight, the heat-resistant porous layer may be excessively densified and ion permeability may be reduced, or the heat-resistant porous layer may become brittle and handling properties may be reduced. This is not preferable.

  In the present invention, examples of the porous substrate formed by including a thermoplastic resin include a microporous film, a nonwoven fabric, a paper-like sheet, and other sheets having a three-dimensional network structure. In particular, a microporous membrane is preferable in that it can be obtained satisfactorily. Here, the microporous membrane has a structure in which a large number of micropores are connected and these micropores are connected, and gas or liquid can pass from one surface to the other. Say the membrane. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is suitable, preferably a polyolefin, and particularly preferably polyethylene. The polyethylene is not particularly limited, but high-density polyethylene or a mixture of high-density polyethylene and ultrahigh molecular weight polyethylene is suitable. For example, in addition to polyethylene, other polyolefins such as polypropylene and polymethylpentene may be mixed and used. In addition, the base material of this invention should just be what consists of a thermoplastic resin 90weight% or more, and may contain the other component which does not affect a battery characteristic of 10 weight% or less.

  In the present invention, the thickness of the substrate is preferably 5 μm or more and 18 μm or less. The porosity of the substrate is preferably 20 to 60%. The Gurley value (JIS P8117) of the substrate is preferably 10 to 500 sec / 100 cc. The puncture strength of the substrate is preferably 10 g or more.

  In the present invention, examples of the heat-resistant porous layer include microporous film-like, non-woven fabric, paper-like, and other layers having a three-dimensional network-like porous structure. From the viewpoint of being obtained, the layer is preferably a microporous film. Here, the microporous film-like layer has a large number of micropores inside, and has a structure in which these micropores are connected. Gas or liquid can pass from one surface to the other. It says the layer that became. In addition, the inorganic filler in the heat resistant porous layer is present in a state of being trapped by the heat resistant resin when the heat resistant porous layer is in the form of a microporous film, and the heat resistant porous layer is a nonwoven fabric or the like. In such a case, it may be present in the constituent fibers or fixed to the nonwoven fabric surface or the like with a binder such as a resin.

  The heat-resistant resin used in the present invention is suitably a polymer having a melting point of 200 ° C. or higher, or a polymer having a melting point of 200 ° C. or higher, preferably aromatic polyamide, polyimide, polyethersulfone, polysulfone, It is at least one resin selected from the group consisting of polyetherketone and polyetherimide. In particular, wholly aromatic polyamides are preferable from the viewpoint of durability, and polymetaphenylene isophthalamide, which is a meta-type wholly aromatic polyamide, is more preferable from the viewpoint of easy formation of a porous layer and excellent redox resistance. is there.

  In the present invention, the heat-resistant porous layer may be formed on both surfaces or one surface of the substrate, but it is preferable to form the heat-resistant porous layer on both the front and back surfaces of the substrate from the viewpoints of handling properties, durability, and the effect of suppressing heat shrinkage. In order to fix the heat-resistant porous layer on the substrate, a method in which the heat-resistant porous layer is directly formed on the substrate by a coating method is preferable. A technique of adhering the quality layer sheet on the base material using an adhesive or the like, a technique such as heat fusion or pressure bonding can also be employed.

  In the present invention, regarding the thickness of the heat resistant porous layer, when the heat resistant porous layer is formed on both surfaces of the substrate, the total thickness of the heat resistant porous layer may be 3 μm or more and 12 μm or less. Preferably, when the heat resistant porous layer is formed only on one side of the substrate, the thickness of the heat resistant porous layer is preferably 3 μm or more and 12 μm or less. The porosity of the heat resistant porous layer is preferably in the range of 60 to 90%.

The separator for a non-aqueous secondary battery of the present invention preferably has a total film thickness of 30 μm or less. The Gurley value (JIS P8117) of the separator is preferably 10 to 1000 sec / 100 cc. The membrane resistance of the separator is preferably 0.5 to ¹⁰ ohm · cm ² . The puncture strength of the separator is preferably 10 to 1000 g.

[Method for producing separator for non-aqueous secondary battery]
In the present invention, the method for producing a separator for a non-aqueous secondary battery is not particularly limited as long as the separator of the present invention having the above-described configuration can be produced. For example, it can be produced through the following steps (i) to (v). It is.
(i) A step of preparing a slurry for coating by dissolving a heat-resistant resin in a solvent and dispersing an inorganic filler therein.
(ii) A step of applying the slurry to at least one surface of the substrate.
(iii) A step of treating the substrate coated with the slurry with a coagulating liquid capable of coagulating the heat resistant resin.
(iv) A step of removing the coagulation liquid by washing with water.
(v) A step of drying water.

  In the step (i), the solvent is not particularly limited as long as it dissolves the heat-resistant resin. Specifically, a polar solvent is preferable, and examples thereof include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. Moreover, the said solvent can add the solvent used as a poor solvent with respect to heat resistant resin in addition to these polar solvents. By applying such a poor solvent, a microphase separation structure is induced and the formation of a heat-resistant porous layer is facilitated. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable. The concentration of the heat resistant resin in the coating slurry is preferably 4 to 9% by weight. In dispersing the inorganic filler in the coating slurry, when the dispersibility of the inorganic filler is not preferable, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable.

  In the above step (ii), the coating slurry is applied to at least one surface of the base material, but when the heat-resistant porous layer is formed on both surfaces of the base material, it is simultaneously applied to both surfaces of the base material. It is preferable from the viewpoint of shortening the process. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a screen printing method, a Meyer bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method. . Among these, the reverse roll coater method is preferable from the viewpoint of uniformly forming a coating film. When applying simultaneously to both sides of the base material, for example, by passing the base material between a pair of Meyer bars, an excess coating slurry is applied to both sides of the base material, and this is applied to a pair of reverse roll coaters. There is a method of precise measurement by scraping off excess slurry in between.

  In the step (iii), the substrate coated with the coating slurry is treated with a coagulating liquid capable of coagulating the heat resistant resin, so that the heat resistant resin is solidified and the inorganic filler is bound. An applied heat resistant porous layer is formed. As a method of treating with the coagulating liquid, a method of spraying the coagulating liquid on the substrate coated with the coating slurry, or a method of immersing the substrate in a bath (coagulating bath) containing the coagulating liquid. Etc. Here, when installing a coagulation bath, it is preferable to install it below the coating apparatus. The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant resin, but water or a solution obtained by mixing an appropriate amount of water with the solvent used in the slurry is preferable. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. When the amount of water is less than 40% by weight, there arises a problem that the time required for solidifying the heat-resistant resin becomes long or the solidification becomes insufficient. On the other hand, when the amount of water is more than 80% by weight, there arises a problem that the cost for solvent recovery becomes high, or the surface that comes into contact with the coagulation liquid is solidified too quickly and the surface is not sufficiently porous.

  The step (iv) is a step of removing the coagulating liquid from the sheet after the step (iii), and a method of washing with water is preferable.

  The step (v) is a step of drying and removing water from the sheet after the step (iv), and the drying method is not particularly limited. The drying temperature is preferably 50 to 80 ° C., and when a high drying temperature is applied, it is preferable to apply a method of contacting the roll in order to prevent dimensional change due to heat shrinkage.

[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, and is characterized by using the separator for a non-aqueous secondary battery having the above-described configuration. The non-aqueous secondary battery has a structure in which a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is impregnated with an electrolytic solution, and this is enclosed in an exterior.

  The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the negative electrode active material include materials capable of electrochemically doping lithium, and examples thereof include carbon materials, silicon, aluminum, tin, and wood alloys. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride and carboxymethyl cellulose. As the current collector, a copper foil, a stainless steel foil, a nickel foil, or the like can be used.

The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _{1/3 O 2, LiMn 2 O 4,} LiFePO 4 , and the like. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride. As the current collector, aluminum foil, stainless steel foil, titanium foil, or the like can be used.

The electrolytic solution has a structure in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4 and the} like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, vinylene carbonate, and the like. These may be used alone or in combination.

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present invention can be suitably applied to any shape.

Hereinafter, the present invention will be described in detail by way of examples.
Various measurement methods in Examples and Comparative Examples of the present invention are as follows.

[Average particle size of inorganic filler]
Measurement was performed using a laser diffraction particle size distribution analyzer (manufactured by Sysmex Corporation, Mastersizer 2000). Water was used as a dispersion medium, and a small amount of a nonionic surfactant Triton · X-100 was used as a dispersant. The central particle size (D50) in the volume particle size distribution was taken as the average particle size.

[Content of water-soluble sodium in inorganic filler]
20 g of inorganic filler was placed in 150 ml of pure water, heated at 80 ° C. for 2 hours, the residue was removed by filtration, and the sodium concentration was measured with a Kotaki flame photometer (ANA-137F). A calibration curve was prepared using sodium oxide (Na ₂ O), and a lithium internal standard solution was used as an internal standard.

[Shutdown (SD) characteristics evaluation]
A separator as a sample was punched into Φ19 mm, dipped in a 3 wt% methanol solution of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P), and air-dried. Then, the separator was impregnated with the electrolytic solution and sandwiched between SUS plates (Φ15.5 mm). As the electrolytic solution, a liquid in which 1M LiBF ₄ was dissolved in a solvent in which propylene carbonate and ethylene carbonate were mixed at a weight ratio of 1: 1 was used. This was enclosed in a 2032 type coin cell. I took the lead from the coin cell, put a thermocouple, and put it in the oven. The cell resistance was measured by raising the temperature at a rate of temperature increase of 1.6 ° C./min and simultaneously applying alternating current with an amplitude of 10 mV and a frequency of 1 kHz. In this measurement, when the resistance value in the range of 135 to 150 ° C. is 10 ³ ohm · cm ² or more, the SD characteristic is judged to be good (◯), and otherwise, the SD characteristic is poor (×). This is shown in Table 1.

[Heat resistance evaluation]
In the evaluation of the above SD characteristics, when the resistance value is maintained at 10 ³ ohm · cm ² or more in the range of 150 to 200 ° C., the heat resistance is evaluated as good (◯), and when it is not The heat resistance was judged to be poor (x), and this is shown in Table 1.

[Flame retardance evaluation]
DSC (differential scanning calorimetry) analysis was performed about the separator used as a sample. A DSC 2920 manufactured by TA Instruments Japan Co., Ltd. was used as the measuring device. The measurement sample was prepared by weighing 5.5 mg of the separator and caulking it in an aluminum pan. The measurement was performed in a nitrogen gas atmosphere at a temperature rising rate of 5 ° C./min and a temperature range of 30 to 400 ° C. When a significant endothermic peak was observed at 200 to 400 ° C., it was evaluated as good (◯), and when it was not observed, it was evaluated as bad (×).

[Evaluation of cycle characteristics]
Using the separators produced in the examples and comparative examples, button batteries were produced as follows.

1) Positive electrode 6 wt% PVdF so that the lithium cobalt oxide (LiCoO ₂ , Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight and PVdF dry weight 6 parts by weight A positive electrode paste was prepared using the NMP solution. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.

2) Negative electrode 6 wt% PVdF so that the dry weight of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Inc.) powder 87 parts by weight, acetylene black 3 parts by weight and PVdF 10 parts by weight as the negative electrode active material An NMP solution was used to prepare a negative electrode agent paste. The obtained paste was applied onto a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.

3) Production of Button Battery A separator (CR2032) having a capacity of about 4.5 mAh was produced by sandwiching the separators produced in Examples and Comparative Examples between the positive electrode and the negative electrode. As the electrolyte, 1M LiPF ₆ EC / DEC / MEC (1/2/1 weight ratio) was used. The manufactured button battery is charged at a constant current (1.6 mA) and a constant voltage (4.2 V) for 8 hours, and discharged at a constant current (1.6 mA) and a constant voltage (2.75 V). 150 charge / discharge cycles were carried out. Table 1 shows the discharge capacity (mAh) of each button battery after 150 cycles.

[Example 1]
1) Production of polymetaphenylene isophthalamide Into a reaction vessel equipped with a thermometer, a stirrer, and a raw material inlet, 753 g of NMP having a moisture content of 100 ppm or less was placed. Was dissolved and cooled to 0 ° C. To this cooled diamine solution, 160.5 g of isophthalic acid chloride was gradually added with stirring to react. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 58.4 g of calcium hydroxide powder was added and stirred for another 40 minutes to complete the reaction, and the polymerization solution was taken out and reprecipitated in water to obtain 184.0 g of polymetaphenylene isophthalamide. .

2) Production of polyethylene microporous membrane As polyethylene powder, GUR2126 (weight average molecular weight 4150,000, melting point 141 ° C) and GURX143 (weight average molecular weight 560,000, melting point 135 ° C) manufactured by Ticona were used. GUR2126 and GURX143 are made to be 1: 9 (weight ratio), and liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd .; Smoyl P-350P; boiling point 480 ° C.) and decalin so that the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent. The composition of this polyethylene solution was polyethylene: liquid paraffin: decalin = 30: 45: 25 (weight ratio).
This polyethylene solution was extruded from a die at 148 ° C. and cooled in a water bath to prepare a gel tape (base tape). The base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes, and then the base tape was stretched by biaxial stretching that was performed in the order of longitudinal stretching and lateral stretching. Here, the longitudinal stretching was 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was 11.0 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, it dried at 50 degreeC and annealed at 120 degreeC, and obtained the polyethylene microporous film. This polyethylene microporous film had a thickness of 12 μm, a porosity of 37%, a Gurley value of 301 sec / 100 cc, and a membrane resistance of 2.6 ohm · cm ² .

3) Manufacture of separator for non-aqueous secondary battery The polymetaphenylene isophthalamide obtained above and a polyethylene microporous membrane are used together with an inorganic filler to manufacture the separator for non-aqueous secondary battery of the present invention. did.
Specifically, aluminum hydroxide having an average particle size of 1.1 μm (manufactured by Showa Denko KK; H-42I) was used as the inorganic filler. When the content of water-soluble sodium in the inorganic filler was measured, it was 37 ppm in terms of Na ₂ O weight.
Then, polymetaphenylene isophthalamide was dissolved in a mixed solvent in which dimethylacetamide (DMAc) and tripropylene glycol (TPG) had a weight ratio of 50:50. An inorganic filler was dispersed in the polymer solution to prepare a coating slurry. The concentration of polymetaphenylene isophthalamide in the coating slurry was adjusted to 5.5% by weight, and the weight ratio of polymetaphenylene isophthalamide to inorganic filler was adjusted to 25:75. Then, two Meyer bars were opposed to each other, and an appropriate amount of coating liquid was put between them. Thereafter, the polyethylene microporous film was passed between Mayer bars on which the coating liquid was placed, and the coating liquid was applied to the front and back surfaces of the polyethylene microporous film. Here, the clearance between the Meyer bars was set to 20 μm, and # 6 was used for both the Mayer bars. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 25: 25 and 40 ° C., followed by washing and drying. This obtained the separator for non-aqueous secondary batteries of this invention in which the heat resistant porous layer was formed in the front and back both surfaces of a polyethylene microporous film.

[Example 2]
As the inorganic filler, aluminum hydroxide having an average particle size of 1.1 μm (Showa Denko; H-42I) was washed with boiling water for 10 minutes, and filtered and dried at 120 ° C. for 2 hours. When the content of water-soluble sodium in the inorganic filler was measured, it was 5 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that this inorganic filler was used.

[Example 3]
As the inorganic filler, aluminum hydroxide having an average particle size of 0.8 μm (Showa Denko; H-43M) was allowed to stand in room temperature water for 5 minutes, and after filtration, dried at 120 ° C. for 2 hours. When the content of water-soluble sodium in the inorganic filler was measured, it was 250 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that this inorganic filler was used.

[Example 4]
As the inorganic filler, magnesium hydroxide having an average particle size of 0.9 μm (Kyowa Chemical Industry Co., Ltd .; Kisuma 5A) was used. When the content of water-soluble sodium in the inorganic filler was measured, it was 3 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that this inorganic filler was used.

[Example 5]
As the inorganic filler, magnesium hydroxide having an average particle diameter of 1.8 μm (manufactured by Kyowa Chemical Industry Co., Ltd .; Kisuma 8) was used. When the content of water-soluble sodium in the inorganic filler was measured, it was 2 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that this inorganic filler was used.

[Comparative Example 1]
As an inorganic filler, aluminum hydroxide (manufactured by Showa Denko; H-43M) having an average particle diameter of 0.8 μm was used. When the content of water-soluble sodium in the inorganic filler was measured, it was 668 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that this inorganic filler was used.

[Comparative Example 2]
As the inorganic filler, aluminum hydroxide having an average particle diameter of 1.1 μm (manufactured by Showa Denko KK; H-42M) was used. When the content of water-soluble sodium in the inorganic filler was measured, it was 371 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that this inorganic filler was used.

[Comparative Example 3]
As the inorganic filler, aluminum hydroxide having an average particle size of 1.1 μm (manufactured by Showa Denko KK; H-42I) was washed with boiling water for 24 hours, and filtered and dried at 120 ° C. for 2 hours. When the content of water-soluble sodium in the inorganic filler was measured, it was less than 1 ppm in terms of Na ₂ O weight.
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that this inorganic filler was used.

As is clear from the results in Table 1, Examples 1 to 5 and Comparative Examples 1 to 3 all have excellent effects in shutdown characteristics, heat resistance and flame retardancy. Then, for Example 1-5, since the content of the water-soluble sodium in the inorganic filler is in the range of 1~300ppm (Na ₂ O weight in terms of) the content of the water-soluble sodium is larger than 300ppm Comparative Compared to Examples 1 and 2 and Comparative Example 3 in which the content of water-soluble sodium is less than 1 ppm, it can be seen that the discharge capacity at 150th cycle is large and the cycle characteristics are excellent.

Claims (7)

A non-aqueous secondary battery comprising a porous substrate formed containing a thermoplastic resin and a heat-resistant porous layer formed containing a heat-resistant resin and laminated on one or both sides of the substrate Separator for
The heat-resistant porous layer contains an inorganic filler that generates an endothermic reaction at 200 to 400 ° C.,
The inorganic filler contains 1 to 300 ppm of water-soluble sodium in terms of Na ₂ O weight, and is a non-aqueous secondary battery separator.   2. The separator for a non-aqueous secondary battery according to claim 1, wherein the inorganic filler is made of a metal hydroxide.   The separator for a non-aqueous secondary battery according to claim 1 or 2, wherein the metal hydroxide is aluminum hydroxide or magnesium hydroxide.   4. The non-aqueous secondary battery separator according to claim 1, wherein the content of the inorganic filler in the heat-resistant porous layer is 50 to 95% by weight.   The heat-resistant resin is at least one resin selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. A separator for a non-aqueous secondary battery according to claim 1.   The non-aqueous secondary battery separator according to claim 1, wherein the thermoplastic resin is a polyolefin.   A non-aqueous secondary battery for obtaining an electromotive force by doping or dedoping of lithium, wherein the non-aqueous secondary battery separator according to claim 1 is used. battery.